[paper] robonwire - design and development of a power line inspection robot.pdf

Robonwire: Design and development of a powerline inspection robot

Milan Jayatilaka, Madhavan Shanmugavel, S.Veera RagavanMechatronics, School of EngineeringMonash University Malaysia campus

Bandar Sunway, Malaysia, 46150{madhavan.shanmugavel, veera.ragavan}@monash.edu

Abstract—This paper presents a design of a low-cost,lightweight powerline inspection robot:Robonwire. Though com-mercial and research robots for inspecting and monitoringpowerline are available, the weight of the robot is high andit requires a lot of human effort during set-up and operation.We focus on developing a laboratory scale robot for powerline inspection. The robot has three arms and a base framewhich houses the electrical and electronic elements to controlthe locomotion and avoiding obstacles. It uses three poweredmotors with wheels one for each arm providing the mobility ofthe robot on the wires. Each arm has two joints. The upper jointconnects the arm body to the wheel assembly while the lower oneconnects the arm body to the base frame. The obstacle avoidanceis achieved by lateral rotation of arms in sequence. This paperpresents the initial phase of the development in which a robotis built for travelling on wire. The motion planning for obstacleavoidance and simulations for torque requirement analysis ofjoint motors are also presented.

Keywords – Powerline inspection robot; Robot; Robonwire

I. INTRODUCTION

Modern power distribution networks are unquestionablycritical in the progress of any nation. Because, they representboth significant investment and critical resource to everycitizen, they necessitate regular inspection and maintenance[22]. Currently, manned or autonomous helicopters are usedto inspect individual sections of the line, a hazardous andgenerally expensive process for energy providers. The useof helicopters for powerline inspection has a long tradition[12], [22], [7], while currently, growing use of unmannedaerial vehicles can be seen [3], [20]. Thus, it is proposed todevelop a low cost, robust, wire scaling robot to conduct theinspections safely and securely under live wire conditions.

A recent development in the field of robotics is the useof robots on wires where robots are used for powerlineinspection. These robots are designed to perform tasks whilemoving on a cable or rope. The ability of these robots tooperate autonomously or to be remotely operated makesthem an attractive solution for jobs involving inspectionand maintenance. The advantages of implementing a roboton wires would be (i) Continuous inspection on live-wire:The robot can be left to operate with minimal interference

with occasional maintenance, (ii) Low risk: The robot canbe put into tele-operation or autonomous mode and inspecthazardous or high value assets without endangering humanlives, and (iii) Higher precision and accuracy: The robotmay provide operators with a greater quantity of accuratetelemetry than would be achievable with periodic inspections.

As such, several such application-specific wire robots havebeen designed in recent years [5], [2], [16], [17], [21],with a majority focussing on high voltage transmission lineinspection and suspension cable inspection. However, otherapplications also exist, for example, (i) structural and cableinspection robots: currently being developed to inspect thesuspension cables on bridges and other structures [8], [6], (ii)Power transmission inspection [14], [16], (iii) Surveillance:Robotic surveillance along wires would allow for a widersurveillance field than static mounted cameras and sensors[24], and (iv) Research: Robots that are designed to travelalong power lines can also be re-purposed to monitor thesizable land areas over which they travel. This data canbe used for forestry research, remote observation, or cropmonitoring.

The scope of this work is limited to modelling design anddevelopment of a robotic platform and the accompanyingelectronics necessary for its motion on the wire. This isthe initial phase of the research which focus on designand development of locomotion mechanism and kinematicanalysis. The main contributions of this paper are:

(i) A laboratory prototype robotic platform is designed forpowerline inspection with three arms with wheels fortraversing on the powerline.

(ii) Kinematic and dynamic analysis of the robot is achievedfor torque requirements.

(iii) The design is focussed on avoiding the largest obstacle:aircraft warning ball while the robot will roll over thesmaller.

(iv) A laboratory scale working prototype is developed forpreliminary testing and experiments.

(v) Arduino based controller is developed for motion con-trol

The paper is organized as follows: The next section II

Proceedings of the 1st International and 16th National Conference on Machines and Mechanisms (iNaCoMM2013), IIT Roorkee, India, Dec 18-20 2013

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discusses the relevant literature in powerline inspection robotand it discusses a review of existing design solutions fromlocomotion standpoint. A brief consideration will be givento articles on the modelling the robot locomotion. Thesection III discusses the physical design and individual sub-components of Robonwire. The section IV presents the se-quence of motions of arms for avoiding obstacles along withstate machine for avoiding obstacle. A simulation study forcalculating torque requirements are presented with kinematicand dynamic analysis of the robot in section V. The paperends with discussions and conclusions in VI.

II. RELEVANT WORK IN POWERLINE INSPECTION ROBOTS

Recently, a significant effort in making powerline inspec-tion robot is seen by industries: Hydro-Quebec, HiBot Corp.,and collaborating Universities. Traditionally, the transmissionline is inspected through visual observation, thermal sensor,by climbing up the tower and foot patrol. The high voltagelines are monitored by helicopter assisted inspection. Thesemethods pose high risk to the operators and line-men andalso inspecting network of powerlines is a time consumingand monotonous job. A recent survey [9], [10] discusses thedifferent types of faults, types of robots used for inspection.

A. LineScount

The LineScout (Fig. 1) weighs 100 Kg is developed byHydro-Quebec for live line inspection [13], [15], [16]. Itcomprises three sections: a wheel frame, a centre frame, andthe arm frame. While facing the obstacle, the robot extendsthe arm frame along the line until it bridged the obstacle,and the raised arms grip the line. Following this, the wheelframe retracts the wheels. The linear actuators shift the centerframe forward along the arm frame and then the wheel frameis shifted further until both wheels were clear off the obstacle.The wheel frame remount its wheels on the line. Finally, theclamps are released, and the arm frame retracts and is shiftedback. The robot continues along its inspection route.

Fig. 1. LineScout Obstacle Avoidance[16]

The design of LineScount utilizes rolling motion, whichenables the robot to simply roll over small obstacles instead

of being forced to avoid them. Apart from the safety clamps,the LineScout did not need to couple or decouple with the linebecause motion of the frames are parallel to the powerline.The wheel frame need only be collapsed or raised. The c.g.of the robot is shifted by sliding the arm and wheel frames inthe centre frame. This minimize the cantilever effect duringobstacle avoidance.

B. Expliner

The Expliner robot (Fig. 2) weighs 84 Kg was developed asa collaboration between the Tokyo Institute of Technology,the Kansai Power Corporation and the HiBot Corporation,from Japan [4]. It has two drive axles with two wheelframes in each. The wheels are driven independently byservo motors. The axles serve as linkages in the robot, and aseparate arm carries a counterweight. The Expliner is rollingover smaller obstacles, while for larger obstacles it pivotson the rear set of the wheels by moving the counterweight.This lifts the front wheels off the line. Now, the front axleis rotated so it is parallel to the line. The entire frame ismoved forward till the front axle is clear of the obstacle. Theprocess is repeated with the rear axle by pivot on the frontaxle, and by moving the counterweight forward. When bothwheels are clear of the obstacle, the robot continues along.The method the Expliner used to traverse obstacles allowedit, like the LineScount to forgo any coupling mechanism:safety clamps. The robot cannot run on other than dual lines,therefore limiting the operation of the robot.

Fig. 2. Expliner Obstacle Avoidance [4]

C. Mobile Robot for Inspection of Power Lines

An older solution [17] to the problem of the line inspectionis shown in Fig. 3. The premise of the article is that, for afully functioning power line inspection robot, the design mustbe able to traverse the largest obstacle on the line: the towersconnected by the lines. Because of the suspended insulatorfor transmission lines employed in British Columbia, theLineScout was able to easily travel across towers using itsexisting obstacle avoidance technology. However, when theinsulators hold the line to the tower axially, the two combined


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insulators form an obstacle too large for most robots. Thisrobot has a fold-able frame which, when unfolded, wouldbe large enough to attach to the tower and move aroundthe insulators to the line on the other side. Much like theLineScout, the frame would remain collapsed until such timeas it was needed. However, the paper claimed to have highestpower to weight ratio with an internal combustion engine.

Fig. 3. Mobile robot for power line inspection [17]

This robot effectively solves one of the biggest problemsin live line inspection. However, given the objectives of thisproject, designing and building a frame that large would adda great deal of weight to the robot, and thereby necessitate amore powerful drive system.

D. Cable Crawler

The robotic solution Fig. 4 built by ETH Zurich [2] issignificantly larger than the above three designs. The cablecrawler travels on a single cable at the top of the mastof electrical tower. The goal of this design was to achievecomplete freedom along the line by reducing the numberof actuators. The robot has large horizontal rollers in bothits front and rear drive units. These drive units held therollers to the lines using spring loaded clamps that enabledthe drive units to widen when passing over the mast head.An additional drive segment was mounted in the middle andused to drive the robot over the masthead itself. The robothad sensor payloads on either side encapsulated in clear PVCspheres.

Fig. 4. Cable Crawler [2]

The cable crawler is capable of continuous motion throughthe line; no obstacle avoidance was necessary because theguide wire upon which the robot moved did not have any

obstacles. The smaller ones could be rolled over. In addition,this setup required merely three motors. Nevertheless, therewere some drawbacks. The design limited the accessibilityof the robot to just the guide wire. Even with the reducedamount of actuators, the design would still expend morepower due to its size.

E. Transmission Line Sleeve Inspection Robot

This robot is developed by by Korea Electric PowerResearch Institute [11]. In contrast to the above robots, itis designed to measure electromagnetic emissions on theline. The robot consists of two parts: drives and the sensorpayload. The sensor payload mount connects to two drives,which are concave caterpillar treads that hug the line. Anouter groove of flexible spines helps to keep the robot onthe line. This robot is not suitable for long distance linemovement. There are no mechanisms to avoid large obstacles.In addition, the robot is very small, and may not be capableof carrying a suitable sensor payload. For its purpose, therobot is well suites. However, it may be difficult to apply therobot to full scale line work.

F. Bipedal Line Walking Robot

A team of Kunshan Institute of Industry Research andUniversity of Hamburg developed an elegant bipedal walkingrobot for powerline inspection [21]. The robot is shown inFig. 5 composed of three segments: two legs, a waist and abody. The waist of the robot is comprised of a revolute jointmounted on the two prismatic joints of each leg. This allowsthe waist to translate along each leg. At the end of each legis a revolute joint that allows the robot to position its feet onthe line. The robot has two locomotion gaits: a flipper stridein which the robot lifts its legs in a striding motion and acrawling stride in which the feet are shuffled along the line.

Fig. 5. Biped Line Walking Robot - CAD representation [21]

The waist actuators are close to the center of mass, therebyminimizing torque on the waist actuators and creating lower


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power consumption. Coupled with the fact that the obstacleavoidance methodology of this robot is a few motions similarto its flipper gait make this design very compelling. However,smooth control of this robot necessitates a fifth order polyno-mial incorporating joint position, velocity and acceleration.

G. Robotic Inspection Over Power Lines (RIOL)

The RIOL is developed by Institute for Systems andRobotics - Lisbon [18], [19] uses gait locomotion. The robothas five degrees of freedom articulated multi-body with asingle prismatic arm in the middle. The robot moves alongthe line by looping two of its claws around the line, the rearinitially clamped securely and the front loosely. Both linksare then extended, thus shifting the front claw along the line.Once this is complete, the front claw clamps securely andthe rear one relaxes. The two links retract, and the rear clawis pulled forward.

Fig. 6. RIOL Robot - CAD representation [18]

To avoid obstacles, the robot uses a stable form of thebrachiation gait [19], a motion commonly employed bygibbons and other primates of interchanging swinging armsfor locomotion. The stable method is to have the prismaticarm of the robot clamp the line and then lower front arm. Therobot then moves forward, shifting the front arm clear of theobstacle. Once this is complete, the middle arm disengagesand the robot moves it clear of the obstacle. Once on the otherside, the robot reattaches the middle arm, and then disengagesthe rear arm. It moves the rear arm clear of the obstacle, andthen reattaches it and disengages the middle arm. By alwayshaving an intermediary connection to the line, the robot isable to swing its forward arm securely past the obstacle.

H. Inspection robot for high-voltage transmission-line

Central South University of Technology, China is devel-oping a mobile robot for powerline inspection [23]. It hastwo arms with two revolute joints each and a wheel drivesmounted their ends. The arms are connected to the base bya prismatic joint, which allows each arm to be extendedto a certain extent. It is claimed that the experimental andsimulated results are identical and this may be due to frictionwas not considered in dynamic model.

I. Comments & summary of existing robots

The design of powerline inspection robot is relativelyyoung research area. It is interesting to note that the opera-

tional environment is well defined, especially the powerlinestructure, and obstacles. The primary challenge is the designof a mechanism which can provide continuous motion on thewire and obstacle negotiation. The two widely used designsare: gait motion or rolling motion. Another challenge ispower to weight to ratio. The weights of most of the robotsare not available, and the two major commercial robots:Linescout and Expliner are too heavy to handle. In viewof the above limitations, we develop a laboratory scaledRobonwire for powerline inspection robot.

III. DESIGN AND DEVELOPMENT OF ROBOT ON WIRE(ROBONWIRE)

The Robonwire (Robot on wire) is a powerline inspectionrobot with wheels and arms mechanisms for locomotion,and obstacle avoidance, because the rolling motion has beenproven to be faster and more secure. The obstacle avoid-ance is achieved through retracting and engaging the armssequentially. Currently, the development is in its initial phasewith the focus characterising the locomotion and obstacleavoidance.

(a) Robonwire - CAD Model

(b) Robonwire - Prototype

Fig. 7. Robonwire - Robon on wire

The Robonwire prototype is shown in Fig. 7 consists ofa base frame on which three arms are mounted. The baseframe houses the control equipment, and power pack. Eacharm is a two-link structure and their joints are driven bya high-torque worm gear assembly. The choice was madefor a worm assembly because of the gearbox’s inherent self-locking nature and the worm gear has high-torque ratio. Inaddition, the gearbox could be driven by a standard, lowpower DC motor, instead of a high powered servo-motor. Thedrive motors are direct drive planetary gear DC motors withbuilt in encoders for localization. In addition, each wheel has


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a safety clamp for stability and security. The clamp closeswhen the robot is rolling along the wire and makes sure thatit does not slip off the line. The gap between each arm isthe maximum obstacle size the robot can accommodate; thearm length is also half of this distance. The biggest obstaclesgenerally found on transmission lines are aircraft markers.These are spherical in shape and measure about 0.75m indiameter [13]. Therefore, while the robot has to accommodatefor the diameter of the sphere laterally, it only has to accountfor the radius height-wise). The Robonwire prototype reducesthe number of moving parts like prismatic joint in Linescoutand more number of linkages in bipedal mechanism orExpliner. The robot uses simple base frame mounted withthree arms with two links. The robot is controlled throughArduino Mega 2560 [1].

A. Arm design

The arm of the robot is shown in Fig. 8. It is designed asa modular unit. The arms are designed to mount the wheelson the line without any coupling or claw mechanisms. Thearm is a two degree of freedom, 3-bar linkage which helpsto position the wheel on the line. The arm is eccentric atthe base so that during obstacle avoidance, the arm may beshifted directly under the body (for a largest obstacle likeaircraft warning ball) of the robot, to maintain the center ofgravity.

Each arm has three parts: a base bracket, the arm body andthe wheel mount. The base bracket is mounted onto the baseframe. It is connected to the arm body through a joint (Lower-Joint). The base bracket houses the lower joint actuator. Thearm body is the main part of the arm and carries the wheelmount at its top through a joint (Upper-Joint). The wheelmount is designed similar to the base bracket and it housesthe drive mechanism of the wheel. In addition and as withthe base bracket, it also holds the upper joint actuator. Forall the joints, a potentiometer feedback system is employedfor position control of the arm. In addition to the drive, thewheel mount also houses the safety clamp. This ensures therobot stays on the line during adverse conditions. It alsoenables the robot to rigidly grip the line while dismountingand reattaching manoeuvres.

Fig. 8. CAD model of Arm, clamp, and wheel-clamp assembly

Each arm has its own control unit for joint actuators, drivemotor and safety clamp servo. Any one controller may beused as a master controller and provide commands to theremaining arms. Since this design is a general purpose roboticplatform, the master controller may be modified to acceptcommands from another, higher level processor. Moreover,the joints are actuated only when the larger obstacles haveto be avoided. Otherwise, only the motors for wheels will bepowered for locomotion.

B. Safety Clamp Design

The robot has one safety clamp shown in Fig. 8 for eacharm. The safety clamp is responsible for securing the robot tothe line. The clamp is composed of two hooks mounted to aservo and its accompanying bracket. The position of the servodetermines the strength of the clamping. For gripping the lineduring obstacle avoidance, the position of the servo may beheightened. Under normal circumstances for rolling down theline, it may position lower. For the obstacle avoidance, theclamp is essential to prevent the robot from tilting too far offthe line and thereby losing grip. From a modelling standpoint,the clamps are enabled during the transition of the robot toovercome obstacles and therefore allow for an assumptionto be made: during transition, the robot arms are rigidlyattached to the line. As visible in the subsequent sections,this assumption allows for a collapsed, extremely simplifieddynamic model that only takes into account of a single armat a time.

C. Wheel design

The wheel design is shown in Fig. 9. Initially, the designwas focused on creating an inner surface that remainedtangent to the line itself. Therefore, the wheel would havebeen constructed from vulcanized rubber of some nature.However, this proved inefficient, as sufficient traction becamean increasingly evident problem. In addition, the fabricationmethod was not feasible. Thus, a machined solution wasrequired.

Fig. 9. Wheel design - CAD model

The new wheel design is conical with an inner lining ofrubber added to provide the necessary traction. The tractionforce on the wheel is proportional to the cosine of the coneangle (φ) from the normal with coefficient of friction µ. The


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reaction forces (FN1 + FN2) is proportional to the normalforce (FN ) [16]:

FN1 + FN2 = µFN

cos(φ)(1)

Therefore, the acuteness of the angle is optimized toaccommodate more cable diameters and the traction force.As a compromise, the angle φ = 45 degrees was set for amaximum usable cable diameter of up to 25 mm.

IV. OBSTACLE AVOIDANCE METHODOLOGY

The CAD representation of obstacle avoidance and thestate machine to execute the obstacle avoidance are shownrespectively in Fig. 10 and in Fig. 11. The obstacle avoidancemethodology is shown with transitions of robot’s arms aroundthe obstacle. The robot is designed to detach the arm closestto the obstacle. The arm folds underneath the robot tomaintain the centre of gravity of the robot. The robot will usethe remaining two wheels to move the entire assembly untilthe front arm is clear of the obstacle. Once this is complete,the robot remounts its forward wheel to the line. This is donefor the remaining arms until all three are clear of the obstacle.

Refer to Fig. 10. When an obstacle is encountered, therobot will release the safety grips from the line. It will thendismount the wheels from the line. Both joints rotate untilthe wheel is flush with the robot’s body and located directlyunderneath the body (only for the largest obstacle - aircraftwarning ball). Once this is complete, the robot uses the drivesthat are still on the line to move the entire robot, includingthe folded front arm, clear of the obstacle. Once the forwardarm is remounted on the line, the process is repeated for thetwo remaining arms until all three of the arms are clear ofthe obstacle.

Fig. 10. CAD representations of obstacle avoidance manoeuvres

The state machine in Fig. 11 shows the sequence of actionsrequired to avoid the obstacle by one arm. To remount theline, the robot will rotate the forward arm counter clockwisewhile unfolding the wheel mount. Sensors placed on thewheel mount will detect the presence of the line. Once theline is detected by the lateral sensor, the arm body will stop

Fig. 11. State Machine for Obstacle Avoidance

rotating. A second sensor will detect the presence of the linevertically and will stop the upper joint. The flag elementsfor the other two arms are used to release their safetyclamp from a stiff grip. The motion sequence of single armis represented by [C + (JU+, JL+), FW+, (JU−, JL−)],where C, JU , JL, FW represent respectively clamp, upperjoint, lower joint, forward motion, and symbol + representsopen and − represents close. The process continues for eacharm.

It is proposed that each arm be controlled individually, withthe flag bits transmitted over a serial interface. In this way,the state machine described here could be implemented oneach microcontroller and the entire operation could be slavedto a higher level controller for tele-operation or feedback.However, the benefits of such a system did not outweighthose of a conventional single controller system. As such,the prototype system will be controlled by an ArduinoMega 2560. The proposed state machine will still providea programming framework for the project.

V. MODELLING & SIMULATIONS

A single arm of the Robonwire is essentially a two-linkplanar manipulator with an eccentric base shown in Fig.12. The corresponding Denavit-Hartenberg parameters aregiven in table I. A kinematic model for a single link can begenerated based on the assumption that the robot is rigidlyattached to the line during obstacle avoidance. As such, thekinematic and dynamic analysis of this robot arm only pertainto the obstacle avoidance phase, in which the robot is eitherremoving or positioning a wheel on the line.

The transformation of a two link manipulator with eccen-


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Fig. 12. Kinematics of arm

TABLE IDH PARAMETERS OF ARM

Link αi−1 ai−1 di θi1 0 l1 0 λ1 + θ12 0 l2 0 θ23 0 l3 0 0

tric base is as follows: cos(β) − sin(λ1 − θ12) 0 l2 cos(λ1 + θ1) + l3 cos(β)sin(β) cos(β) 0 l2 cos(λ1 − θ1) + l3 cos(β)

0 0 1 00 0 0 1

(2)

where λ1 is the offset angle between the base of the bracket andthe arm joint, θ1, θ2 are joint variables, and l2, l2, l3 are the lengthsof the base bracket, arm body and wheel mount respectively andβ = λ1 + θ12, and θ12 = θ1 + θ2.

Thus, the Jacobian J is given by:

J =

(−l2 sin(λ1 + θ1)− l3 sin(γ) l3 sin(γ)l2 cos(λ1 + θ1) + l3 cos(γ2) l3 cos(γ)

)(3)

where γ = λ1 − θ1 + θ2Then the joint torques can be computed as:

τ = JT (θ1, θ2)F (4)

Given the nature of the robot, the forward motion of the robotwith the folded arm clear off the obstacle may be modelled as asingle prismatic joint, with infinite length. However, for the remountand dismount motions, the above model of a single arm is sufficient.

In order to develop the controller for the system, the equation ofmotion of the arm is derived using Lagrangian analysis.

Let ri be the center of mass for link i using the link frame, Iibe the inertial tensor for link i acting at the Centre of Mass (CM),and mi be the mass of link i acting at the CM. The positions andvelocities of the link CMs are:

x2 = l1 cosλ1 + r2 cos θ1 (5a)y2 = l1 sinλ1 + r2 sin θ1 (5b)x3 = l1 cosλ1 + l2 cos θ1 + r3 cos(θ12) (5c)y3 = l1 sin θ1 + l2 sin θ1 + r3 sin(θ12) (5d)

where θ12 = θ1 + θ2

x2 = −r2 sin θ1θ1 (6a)y2 = r2 cos θ1θ1 (6b)x3 = −(l2 sin θ1 + r3 sin(θ12))θ1 − r3 sin(θ12)θ2 (6c)

y3 = (l2 cos θ1 + r3 cos(θ12))θ1 + r3 cos(θ12)θ2 (6d)

The kinetic energy of the system is:

T =1

2m2v

22 +

1

2I2ω2 +

1

2m3v

23 +

1

2I3ω3 (7)

where v2i = x2i + y2i .Since the arm is constrained in x− y plane, Ii = Iiz , ω2 = θ2,

and ω3 = θ1 + θ2.

T =1

2m2(x

22 + y22)+

1

2I2z θ

21 +

1

2m3(x

23 + y23)+

1

2I3z (θ1 + θ2)

2

(8)Kinetic energy:

T (θ, θ) =1

2I3z (θ1 + θ2)

2 +1

2m2(r

22x1)

2 +1

2I2z θ

21+

1

2m3(l2θ

21 + 2l2c2(θ

21 + θ1θ2) + r23(θ1 + θ2))

2)(9)

Potential energy:

P =∑

mighi = m1gr1 sin(λ1) +m2g(l1 + r2s1))+

m3g(l1 + l2s1) + r3s1,2)(10)

Using the above two equations in Lagrangian equation of motion:

d

dt

∂L

∂qi+∂L

∂qi= 0 (11)

where L = T − P is Lagrangian,

θ1(m2r22 +m3l2 + 2l2m3c2 +m3r

23 + I3z ) + θ1θ2(−l2m3s2)+

θ2(m3r23 + I3z )−m2gr2c1 −m3g(l2c1 + r3c1) = 0

θ2(I2z +m3r23 + I3z ) + θ1θ2m3l2s2 + θ1(m3l2c2 +m3r

23

+I3z )−m3gr3c2 = 0(12)

where c2 = cos θ2, c1 = cos θ1, s1 = sin θ1, s2 = sin θ2The torque requirements are simulated using the data from

SolidWorks R©. It is found that the torque requirement of the upperjoint is lesser than the lower motor. Intuitively, this is correct andhence the design is validated. This helps in selection of motors as


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Fig. 13. Torque of upper actuator joint for 180 degree motion

Fig. 14. Torque of lower actuator joint for 180 degree motion

described in Sec. III. The calculated moment of inertia (gm-sqmm)of arm from the CAD model is:[

Ixz Ixx IxyIyz Iyx IyyIzz Izx Izy

]=

[0 0.218e6 −0.25e60 −0.25e6 19.23e6

19.19e6 0 0

]

VI. DISCUSSIONS & CONCLUSIONSThis paper presents initial design of prototype of a powerline

inspection robot: Robonwire. The aim of the robot design is to makeit low-cost & lightweight. In this phase, a robot is built for travellingon wire. A detailed design for motion and sequence of control forobstacle avoidance is presented. The design modelling and analysisof single arm has been completed. Torque requirements for robotjoints are simulated with CAD data. It conforms to the designrequirement that the lower joint needs higher torque than the upperjoint. The prototype robot is able to travel on the wire. Currently,sensor based obstacle avoidance and shifting of robot’s centre ofmass during obstacle avoidance are under study. Sensor integration,navigation, and telematics are planned for future developments.It is believed that this design will be a more effective solutionto the problems that line working robots to maintain and inspectwidespread transmission lines. In addition, optimization of design,motion sequence and sensors and actuators are planned in future tomake this robot platform robust and cost-effective.

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